1. Field of the Invention
The present invention relates generally to communications systems and more particularly to equalization apparatus and adaptation methods for automatically eliminating pre-cursor inter-symbol interference caused by a serial communication channel for a binary, Non-Return-to-Zero (NRZ), serial data stream without requiring transmit pre-equalization.
2. Description of the Related Art
Many communications and computing systems use serial transceivers to interconnect high bandwidth devices. The data bits of the communications and computing systems may be processed in groups, such as bytes or words, but transmitted as a series of bits. The serial transceivers separate and aggregate the bits in a device referred to as a Serializer/Deserializer (SerDes). In a typical Serializer/Deserializer (SerDes) application, the biggest challenge is to guarantee that every transmitted data bit is correctly received. In the case of backplane transceivers that must operate above 1 Gb/s data rates, the loss and dispersion characteristics of the channel make it so that a certain amount of signal conditioning is required in order to recover the channel impaired signal arriving at the receiver without error.
One form of channel impairment is inter-symbol interference, generally caused by dispersion of the signal as it travels along the channel. A data pulse travelling over a channel is dispersed or smeared by stretching the pulse such that it extends over a longer duration when it exits the channel than it extended when it was introduced into the channel. The stretched pulse can be thought of having pre-cursor and post-cursor distortions and these pre-cursor and post-cursor distortions result in inter-symbol interference. The inter-symbol interference caused by pre-cursor distortion can be easily corrected by using pre-emphasis in the transmitter, but for a fully adaptive system, this would require an out-of-band or in-band communication link between the receiver and the transmitter. Thus, a limitation of this system is the fact that the transmitter co-efficients must be updated and set as a function of the channel, and as such can only be adapted based on criteria that is obtained in the receiver. For the system to be fully adaptive, update information must be passed from the receiver to the transmitter in an out-of-band or in-band fashion.
However, providing such a communications link between the receiver and transmitter is unattractive in certain applications. For example, there may be interoperability issues in some applications that do not provide specific methods for receiver-to-transmitter communication.